As described in U.S. Pat. No. 6,708,562, an oil-level indicator is mounted on the oil expansion vessel of an electric power transformer, choke or tap changer in which a float is operatively connected to a float rod that converting the vertical movement of the float to the rotation of the float shaft in turn connected with a display shaft carrying an indicator or pointer which rides on or over a scale, This displays shaft in also via a transmission, e.g. a belt, to an input shaft carrying an angle encoder of an electromagnetic type having a magnetic hub which cooperates with a contactless pick-up in the form of a Hall element with integrated ASIC to form an ASIC Hall sensor, converting the position of the magnetic actuator into an absolute incremental or sine-cosine output signal.
Such a gauge or indicator is highly effective but, as a result of its angle encoder, is relatively expensive. The separate mounting of the angle encoder on the angle-encoder shaft with the necessary coupling to the display shaft carrying the pointer increases the complexity, expense, and likelihood of failure of the device.